Pressure exchangers



July 23, 1957 4 G. JENDRASSIK 2,800,120

' PRESSURE EXCHANGERS Filed Nov. 10, 1954 3 Sheets-Sheet l FOE.2.

mYmmd g W OR y 7 G. JENDRASSIK PRESSURE EXCHANGERS 3 Sheets-Sheet 2 Filed Nov. 10, 1954 kw kw \h aw I- III Frill 4 2112B%,M Mike y 1957 G. JENDRASSIK PRESSURE EXCHANGERS 3 Sheets-Sheet 5 Filed Nov. 10, 1954 MzmEQ \All QM OV United States Patent PRESSURE EXCHANGERS George .lendrassik, deceased, late of London, England, by Andre Gabor Tihamer Boszormenyi, London, England, and Clara Jendrassik, executors, London, England, assignors, by mesne assignments, to Jendrassik Developments Limited, London, England Application November 10, 1954, Serial No. 468,094

Claims priority, applications Great Britain November 30, 1953 and December 11, 1953 13 Claims. (Cl. 123-119) The invention relates to rotary pressure exchangers of the kind comprising a ring of cells for the compression and expansion of gas, ducting for leading gas to and from the cells (for example, at heat input and heat rejection stages) and means for effecting relative rotation between the cells and the ducting; which ducting, during operation of the pressure exchanger, co-operates with the cells to form a low pressure zone in which lower pressure scavenging occurs and a high pressure zone in which high pressure scavenging occurs. The invention is also concerned with a method of operating such pressure exchangers.

By the term scavenging is meant the discharge and replacement by other gas of at least part of the gas content of a cell. The discharge and replacement processes for a cell may take place simultaneously or in succession.

The invention is particularly concerned with pressure exchangers of the above kind which are employed to supply a consumer machine with gas at a high pressure or velocity. Such a pressure exchanger could be employed, for example, for supercharging an internal combustion engine. In this case it would be desirable for the supercharging air to be comparatively clean i. e. uncontaminated with soot or other foreign matter. It may also be desirable that the air or other gas supplied by the pressure exchanger should undergo as small a temperature rise as possible in the pressure exchanger. An object of the present invention is to provide an improved pressure exchanger and method of operation therefor by which these desirable conditions may be produced. I w

According to the present invention there is provided a pressure exchanger comprising a ring of cells for the compression and expansion of gas, ducting for leading gas to and from the cells and means for effecting relative rotation between the cells and the ducting, the ducting including high pressure scavenging passages which co-operate with cells to form a high pressure scavenging zone and lower pressure scavenging passages which cooperate with cells to form a low pressure scavenging zone, the passages being so arranged and dimensioned that, during operation of the pressure exchanger, the cells of the high pressure scavenging zone are incompletely scavenged and that flow of gas through the cells of the high pressure scavenging zone is in a direction opposite to that of the flow of gas through the cells of the low pressure scavenging zone.

Preferably the gas-flow through the cell ring is between two opposed end faces of the cell ring and the scavenging passages comprise, at one end face of the cell ring, a high pressure introduction passage for high pressure gas and a low pressure extraction passage for low pressure scavenged gas and, at the other end face of the cell ring, a low pressure introduction passage for low pressure scavenging gas and a high pressure extraction passage for a useful supply of gas.

ICC

A pressure exchanger according to the invention is particularly applicable to supercharging an internal combustion engine, the said high pressure introduction passage then being connected to an exhaust manifold of the engine, and said useful gas extraction passage being connected to an induction manifold of the engine and the low pressure scavenging passages being open to the atmosphere. As the high pressure and low pressure scavenging gas streams flow in opposite directions through the cells, the supercharging gas flowing from the useful gas extraction passage of the pressure exchanger is substantially fresh air which has been drawn in through the low pressure scavenging passage and is therefore comparatively cool and free from soot or like foreign matter which might be present in the high pressure scavenging-gas i. e. the exhaust gases from the internal combustion engine. Also by arranging the pressure exchanger so that the high pressure scavenging is incomplete, the fresh air content of the supercharging gases is increased and contamination by the engine exchaust gases is reduced. Preferably the low pressure scavenging is complete or substantially complete; but it may be incomplete provided contaminated exhaust gases in the cells are not allowed to approach too near to the low pressure introduction passage and contaminate the fresh air introduced thereby.

The pressure exchanger according to the invention may also include pressure-responsive means whereby high pressure scavenging or scavenged gas may pass directly from the high pressure zone into the low pressure zone e. g. at gas pressure differences therebetween above a predetermined value. The pressure responsive means may be positioned between the scavenging passages at the high pressure gas introduction end face of the cell ring, thereby constituting a pressure responsive relief valve whereby high pressure scavenging gas may by-pass the cell ring. Preferably the pressure responsive means may be so arranged as to introduce high pressure gas, by-passing the cells, into the low pressure scavenging passages in the direction of scavenging gas-flow therein thereby promoting further scavenging. The pressure repsonsive means preferably includes a spring controlled valve.

In order to permit relative rotation between the cell ring and the associated ducting of a pressure exchanger it is necessary to leave a clearance'space therebetween. Normally the cell ring is constituted by a cylindrical rotor containingcells spaced around the periphery of the rotor and extending axially thereof and the associated structure is stationary and includes end plates facing cell openings in the ends of the rotor and carrying the ducting. It is possible, however, to make the cell ringstationary and to rotate the ducting. The clearance spaces between the associated structure and the cell ring are made as small as possible in order to restrict the leakage of working gas through the spaces. Sealing means such as labyrinth seals may be provided to further restrict the leakage of working gas but if that gas is hot or is contaminated by soot, dust or the like, the seals or the clearance spaces may be clogged or distorted and the cell ring or end plates damaged. A further object of the invention is to provide improved sealing means between the cell ring and the associated ducting tending to prevent or considerably restrict leakage of the working gas into the clearance space or spaces.

A pressure exchanger according to the invention may have therefore means for introducing sealing gas into a clearance space between the cell ring and the ducting, the pressure of the sealing gas being higher than that prevailing in the region of introduction of the sealing gas, whereby working gas in the cells or ducting is prevented or restricted from flowing into the said clearance space.

The sealing gas may be extracted from the pressure exchanger itself from a passage or cell at a higher pressure than that prevailing in the clearance space. The sealing gas may be introduced throughout the whole of the sealing space or it maybe introduced at several positions spaced apart in a clearance space. Where the sealing gas is introduced at several positions in the clearance space, the sealing gas may be at several different pressures in accordance with the pressures prevailing in the regions of introduction of the sealing gas. The sealinggas at different pressures may be obtained from different parts of the pressure exchanger. Preferably the pressure of the sealing gas is only slightly greater than the pressure prevailing in the passage or cell, whose contents are required to be sealed from the clearance space, so that only a small quantity of the sealing gas will flow into the said passage or cell. Instead of extracting the sealing gas from the pressure exchanger it may be provided by a source externally thereof e. g. from an air compressor or compressed air reservoir. 7

In a preferred embodiment of the invention the cell ring is carried by a cylindrical rotor and the associated ducting includes stationary end plates spaced from the ends of the rotor thereby leaving clearance spaces between the end plates and the cell ring, the end plates having annular flanges extending therefrom and embracing in a'telescopic manner the rotor so as to leave an annular clearance space between the flanges and the cylindrical surface of the rotor.

The invention also consists in a method of producing a supply of compressed gas (for example, air for supercharging an internal combustion engine) by using a pressure exchangercomprising a ring of cells for the compression and expansion of gas, ducting for leading gas to and from the cells and means for effecting relative rotation between the cells and the ducting, the ducting including high pressure scavenging passages which co-operate with cells to form a high pressure scavenging zone and low pressure scavenging passages which co-operate with cells to form a low pressure scavenging zone, whichmethod consists in passing the high pressure and low pressure scavenging gas through the cells of the two scavenging zones respectively in opposite directions and producing incomplete scavenging of the high pressure scavenging zone.

By way of example, the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a peripheral development of the pressure exchanger showing the pressure exchanger employed for supercharging an internal combustion engine;

Figure 2 is an enlargement of part of Figure 1 and shows a pressure-responsive by-pass valve;

Figure 3 is an axial sectional view of the pressure ex: changer;

Figure 4 is part of an axial sectional view similar to Figure 3 and showing a modification;

Figure 5 is a view on the line VV in Figure 4 and Figure 6 is a part of an axial sectional view similar to Figure 4 and showing a further modification.

In Figure 1 the reference 1 denotes a cell ring moving relatively to ducting in the direction of arrow 2; The individual cells are denoted reference 3 and have ends 3 and 3 which during operation of the pressure exchanger come into communication with passages carried by end plates 4' and 4" respectively. End plate 4 has therein a passage 5 through which flowsincorning fresh air' (i. e. the aforesaid low pressure introduction passage for lo'w pressure scavenging gas) and passage 6 for compressed air leaving the cell ring (i. e. the aforesaid useful gas extraction passage). End plate 4" has therein a passage 7 for the expelled low pressure gas (i. e. the aforesaid low pressure extraction passage for low pressure scavenged gas) and a passage 8 forhigh pressure gas entering the cells (i. e. the aforesaid high pressure introduction passage for high pressure gas). The compressed air passage is connected to a consumer device 9, which in this example is an internal combustion engine to be supercharged. The connecting conduit 6' is connected to the induction manifold of the engine. A further conduit 8' connects the exhaust manifold of the engine to the high pressure introduction passage 8 of thepressure exchanger.

The operation of the pressure exchanger is as follows: cells leaving the region of the high pressure scavenging passages 6 and 8 contain partly heated or contaminated gas i. e. the exhaust gases of the internal combustion engine, at a pressure higher than that prevailing in passages 5 or 7, and so on arriving at the passage 7 gas in the cells flows out through the ends 3" into the passage 7. By the time the pressure has fallen suificiently in the cells, the ends 3 have been opened towards the passage 5 by the forward movement of the cell ring in the direction of arrow 2. Fresh air then enters the cells and when the ends 3" of the cells reach that portion of the end plate 4" between the passages 7 and 8, the cells become closed towards passage 7. The ends 3' of the cells are closed somewhat later than the ends 3 so that pressure impulses are set up in thecells whereby compression of the air in the cells takes place. The cells then travel on in the direction 'of arrow 2 and when they are opposite the end of the passage 8, the ends 3 are opened towards that passage and since the gas therein is at a higher pressure than that prevailing in the cells there is a flow of hot gas from passage 8 into the cells through the ends 3". The pressure therein is raised and the gas therein is set in motion. This has the efiect that a pressure impulse travels through the cells from passage 8 towards the closed ends 3 of the cells. When the ends 3' are opened a certain amount of compressed air leaves the cells and flows through passage 6 to the internal combustion engine 9. The exhaust gases of the internal combustion engine are in a heated state and pass through conduit 8' back to the passage 8. Instead of setting up a pressure impulse in the cells aligned with the passage 8, the flow through the passage may be produced by other effects, for example by the action of a fan positioned in the passage or by the pumping action which may be caused by the supercharged internal combustion engine when the ends 3 of the cells are open. The passages 3 and 6 are then evered from the cells either simultaneously or one after the other and the cells containing gas at a somewhat elevated pressure move forward in the direction of arrow 2 into the low pressure zone. The low pressure scavenging takes place under the effect of the impetus produced by the out-flow from the cells into passage 7 promoted by the suction effect in passage 7 or by other means, for example, a fan positioned in any suitable part of the ducting constituting the passages. In accordance with the invention the low pressure and high pressure scavenging gases have been arranged to flow in opposite direct-ions as shown in the figure. The clean fresh air enters the cells through the passage 5 on the same side of the cell ring as the compressed air leaves through passage 6 and the hot or contaminated gas enters the cells through passage 8 on the same side of the cell ring as the low pressure scavenging gas leaves through passage 7. The scavenging at the low pressure zone is made complete or as competer as possible and the scavenging at the high pressure zone is made incomplete. The pressure exchanger is operated in such a way that the path of the front of the volume of air entering the cells through the passage 5 should reach during scavenging the far end of the cells as shown by the dotted line 11. In practice some mixing will inevitably occur and so it is desirable that the path of the front of the volume of air should overshoot the cells and this has been shown by the dotted line 12. It is possible that the pressure'exchanger could be operated with incomplete scavenging at the low pressure zone, but care would have to be taken to ensure that contaminated gases do not penetrate too far into the cells thereby contaminating the fresh air taken inat passage 5. On the other hand at the high pressure zone the path of the front of the gas entering the cells through duct 8 should not r reach the far end of the cells, so that partial scavenging must take place. This has been shown by the dotted line 13. It is preferable to allowrnot more than half of the gas contained in the cells, before they have come into contact with duct '8, to enter into duct 6. By this means contaminated gas in the duct 8 will not pass out through the duct 6 and instead the compressed air passing out through duct 6 will be the air taken in through duct 5 and compressed in the cells between the ends 3' of the cells and the lines 11 or 12 and 13. By causing at least half of the fresh air intake to remain in the cells when passage 6 is reached, a buffer layer of clean air is provided in the cells to separate the contaminated gas from the cool fresh air, which is taken in at 5 and after immediate compression ejected at passage 6.

The described method of counter-flow scavenging whereby the low and high pressure scavenging flows take place in opposite directions also reduces the heating of the cool air charge by the cell partitions since the cell ends by which the cool air enters are themselves cool and do not come into contact with hot gases.

The scavenging air entering from the atmosphere might be carrying dust or the like, and therefore an air cleaner or filter may be arranged in the high pressure passage 6 leading the compressed gas to the internal combustion engine or other consumer device 9. By this arrangement only the useful gas supplied to the consumer has to pass through the cleaner. The cleaner is placed in passage 6 rather than in passage 5 as a considerably greater quantity of air passes through passage 5 than passage 6.

It is preferable not to extract compressed gas from the high pressure ducting i. e. passages 8, 8, 6 or 6' since higher pressures may be obtained thereby. Should however the conditions be such that the extraction of gas is permissible this can be effected by extracting gas through valve-controlled conduit 14. Such gas extraction would be permissible if, for example, the pressure in passage 6 and conduit 6 was too high. In accordance with the in- Vention however the pressure in the high pressure ducting may be relieved by valve 15 shown in Figure 2. This valve comprises a valve member 15 pivoted at 16 and urged in a closed position by a spring 18 engaging a washer 19 and lever arm 20 integral with the valve member 15. When closed the valve member 15 lies across a by-pass passage 17 in a wall positioned between the passage 8 and the passage 7. When pressure in the passage 8 exceeds a certain value predetermined by the stiffness of the spring 18, the valve member is forced away from its closed position and the high pressure gas flows through the bypass 17 into the passage 7. The valve member 15 is pivoted to the wall of passage 7 downstream of the bleed passage 17 so that the high pressure gas flowing therethrough is introduced into the passage 7 in the direction of flow of the low pressure scavenged gas flowing therein, in order to further promote the low pressure scavenging. The by-pass and valve need not necessarily be positioned in the wall 10 and may for example be arranged between passages 6 and 5.

The pressure exchanger shown in the Figures 1 and 2 is of a simple design but the invention can be applied to pressure exchangers of more complicated design. Transfer channels by which gas from cells leaving the high pressure zone may flow into other cells approaching that zone may be provided. The cell ring may be rotary and the ducting stationary or vice versa and also the geometric form of the cells may be different. For example, they may be helicoidal or arranged on the surface of a cone and their openings could be in a plane other than that perpendicular to the axis of the ring.

Referring now to Figure 3 the cell ring 1 is rotatable relatively to end plates 4' and 4" about stub shafts 21 and 22' supported in bearings 21 and 22, respectively, in the end plates. End plate 4' accommodates passage 6 for relatively cool and clean high pressure air for supercharging the internal combustion engine (not shown in this figure) and passage 5 for low pressure air drawn in from the atmosphere. End plate 4" accomodates passage 8 for hot exhaust gas from the engine which gas is possibly contaminated with soot or the like, and passage 7 for low pressure gas to be discharged to atmosphere. The exhaust gas should not flow into the clearance spaces between the cell rings and the end plates, contact certain parts of the pressure exchanger, nor mix with the clean low pressure gas. End plate 4 has a tubular flange 23 which embraces the cylindrical surface of the rotor 1 and end plate 4" has a tubular flange 24 which embraces the flange 23 of end plate 4'. The flanges 23 and 24 are accurately positioned relatively to each other in the manner of a telescope leaving two annular spaces between the cylindrical surface of the cell rotor 1 and the inner flange 23 and between the inner flange 23 and the outer flange 24 respectively. The space inside the outer flange is sealed from the outside of the pressure exchanger by sealing rings 28 and communicates with the space between the inner flange 23 and the rotor 1 through hole 37.- The inner annular space is bounded at the axial ends of the cylindrical surface by labyrinth seals 26, 26, 26" and 26". The end plates 4 and 4" are spaced apart from the ends of the rotor 1 by small clearance spaces, the axial width of those clearance spaces being maintained by the bearings 21 and 22 and the telescoped flanges 23 and 24. Labyrinth seals 25, 25, 25", 25" are provided on the end faces of the rotor 1. End plate 4" is water cooled by internal chambers 27 therein. Conduits 35, 36 resiliently telescoped together connect high pressure passage 6 with the annular spaces, compressed air thus being tapped off by the conduits 35, 36 to flow into the annular spaces as sealing gas which flows past the labyrinth seals into the clearance spaces between the end plates and the rotor. End plate.4' has a circular groove 29 in the face adjacent the end of the rot-or 1, the groove 29 being open towards the labyrinths 25 and 25. The groove 29 communicates with passage 6 through channel 30 and with a central space within the rotor 1 through channels 31. Similarly there is a circular groove 32 in the end face of end plate 4 facing the other end of the cell rotor, the groove 32 being open towards labyrinths 25" and 25, and connected to the central space in the cell rotor 1 through channels 31. It will therefore be appreciated that the circular groove 32 is in contact with the passage 6 through channels 31', 31 and 30. Thus compressed air in the passage 6 is extracted through channel 30 to emerge through circular grooves 29 and 32 as sealing gas. The sealing gas leaves the clearance spaces through circular spaces 33, 33 around the stub shaft roots, and then passes through channels 34, 34' into the low pressure passages 5 and 7 respectively. Connecting pipes 46, 47 connect the passages in the end plates -to the engine manifolds and air inlet and outlet respectively.

During operation of the pressure exchanger, the pressure prevailing in passage 6 is higher than that in passage 8 and as a result sealing gas flows into the annular spaces between the flanges 23 and 24 and between the flange 23 and the rotor 1 and also through the circular grooves 29 and 32 into the end clearance spaces leaving through channels 34, 34. The gas pressure in the clearance space adjacent the passage 8 is higher therefore than in the passage itself and thus substantially no hot contaminated exhaust gas from the engine will leak out from the passage 8 into the clearance space. In practice a small amount of air will be found to flow from the clearance space towards the passage 8. It is desirable that the pressure of the sealing gas in the vicinity of the passage 8 should only be slightly greater than the pressure in the passage itself. The pressure exchanger described with reference to Figure 3 can supercharge the engine therefore with no or substantially no contamination of the air by engine exhaust gases in view of the opposed scavenging flow hereinbefore described and in view of the sealing by air bled from the compressed air passage 7,

If there is noneed to compensate for axial movement between the end plates and the rotor e. g. movement caused by thermal expansion or contraction, a simple casing may be provided around the rotor 1 instead of the telescopic flanges 23 and 24. The end plates would be secured to the casing and the sealing gas would be introduced from the passage 6 into the casing through a suitable conduit. The conduit may be made telescopic as are conduits 35, 36 or may be a simple pipe. The circular grooves 29 and 32 may be provided on the rotor instead of on the end plates as before. Alternatively they may be formed around the stub shafts 21' and 22', if labyrinth seals are also provided thereon. I

If the sealing gas is supplied by an outside source, then conduit 36 and grooves 29 and 32 will have to be connected with the source. A modification in which sealing gas may be supplied from a source externally of the pressure exchanger or from the pressure exchanger itself is shown in Figures 4 and 5. Grooves 38 and 39 are provided on the end plate 4" or on other parts not moving relatively to the hot gas passage 8, for example rotor casing 40. Grooves 38 and 39 need not be formed around the whole of the circumference; but .instead may be formed only on parts thereof where the sealing by the sealing gas is necessary. These grooves are connected by ducts 41 which are supplied with sealing gas from the external source or from the pressure exchanger itself. The pressure of the gas is higher than that prevailing in passage 8. Labyrinth seals 26, 26, 26", 26" are provided between the cylindrical surface of the cell rotor and the casing 38 and labyrinth seals 25, 25", 25' are provided between the rotor and the end plates or on the roots of the stub shafts 21' and 22'. With the arrangement just described the loss by leakage of the'sealing gas would probably be lower than that with the arrangement shown in Figure 3-.

lf several passages, with different pressure prevailing in them, have to be sealed, the sealing can well be achieved by using the modifications shown in Figures 4 and 5, if in the respective conduits 41, sealing gas of pressure slightly higher than that in the associated passage is introduced. It is further advantageous to provide some sealing arrangements e. g. labyrinths 42, 42' between grooves 38 and 39 and the passage.

In Figure 6 there is shown a further modification in which the cell rotor is sealed by labyrinths 44 provided on a-radially protruding annular face 43 of the rotor structure and the groove 38 is accommodated in end plate 4".

In the embodiments described herein the labyrinth seals may be replaced by any other suitable seals.

What is claimed is:

1. A pressure exchanger comprising in combination a first and a second element mounted co-axially for relative rotation and means for effecting said relative rotation, said first element defining a ring of open-ended cells extending therethrough between two opposed faces thereof, said second element including low pressure inlet means to allow the introduction of low pressure fluid into said cells, high pressure outlet means to allow the extraction of high pressure fluid from said cells, said high pressure outlet means and said low pressure inlet means being circumferentially spaced from each other and both positioned adjacent one face of said first element, low pressure outlet means to allow the extraction of low pressure fluid from said cells and high pressure inlet means to allow the introduction of high pressure fluid into said cells, said low pressure outlet means and said high pressure inlet means being circumferentially spaced from each other and both positioned adjacent said other face of said first element, said low pressure inlet and outlet means together defining a low pressure scavenging zone and said high pressure inlet and outlet means together defining a high pressure scavenging zone, in

which latter zone the scavenging of said cells is incom- I i a ZJ A pressure exchanger as claimed in claim 1 in which; scavenging in said low pressure scavenging zone is substantially complete. e V V 3;. A pressure exchanger comprising in combination a first and a second element mounted co-axially for relative rotation and means for effecting said relative rotation, said first element defining a ring of open-ended cells extending therethrough between two opposed faces thereof, said second element including low pressure scavenging means comprising a low pressure inlet duct to allow the introduction of low pressure fluid into said cells and a low pressure outlet duct to allow the extraction of low pressure fluid from said cells, high pressure scavenging means providingincomplete scavenging and comprising a high pressure inlet duct to allow the introduction of high pressure fluid into said cells and a high pressure outlet duct to allow the extraction of high pressure fluid from said cells, said low pressure inlet duct and said high pressure outlet ductbeing positioned adjacent one face of said first element and circumferentially spaced from one another and said low pressure outlet duct and said high pressure inlet duct being positioned adjacent said other face of said first element and circumferentially spaced from one another, and pressure-responsive bypass means positioned between said high pressure scav enging means andsaid low pressure scavenging means externally of said first element; e

4. A pressure exchanger comprising in combination a first and 'a second element mounted co-axially for relative rotation and means for effecting said relative rotation, said first element defining a ring of open-ended cells extending therethrough between two opposed faces thereof, said second element including low pressure inlet means to allow the introduction of low pressure fluid into said cells, high pressure outlet means to allow the extraction of high pressure fluid from said cells, said high pressure outlet means and said low pressure inlet means being circumferentially spaced from each other and both positioned adjacent one face of said first element, low pressure outletmeans to allow the extraction of low pressure fluid from said cells, high pressure inletmeans to allow the introduction of high pressure fluid into said cells, said low pressure outlet means and said high pressure inlet means being circumferentially spaced from each other and both positioned adjacent said other face of said first element, said low pressure inlet and outlet means together defining a lowpressure scavenging zone and said high pressure inlet and outlet means together defining a high pressure scavenging zone, in which latter zone the scavenging of said cells is incomplete, and pressure-responsiveby-pass means positioned between said high pressure inlet means and said low pressure outlet means, externally of said first element.

5. A pressure exchanger as claimed in claim 4 in which said pressure-responsive by-pass means includes a directing member capable of directing fluid from said high pressure inlet means into said low pressure outlet means substantially in the direction of fluid flow in said low pressureoutlet means.

6. Apressu-re exchanger as claimed in claim 4 in which said pressure-responsive by-pass means comprises a passage interconnecting said high pressure inlet means and said low pressure outlet means externally of said first element, a flap valve positioned at the end of the passage adjacent said low pressure outlet means to close said passage except when a predetermined fluid pressure is attained therein and a spring arranged to hold said flapvalve closed until the predetermined pressure is attained, said flap valve when open being capable of directing fluid from said passage into said low pressure outlet means substantially in the direction of fluid flow therein. I

7. A pressureexchanger comprising in combination a first and a second element mounted co-axially for relative rotation, a plurality of clearance spaces between said elements and means for efiecting said, relative rotation, said first element defining a ring of open-ended cells ex tending therethrough between two opposed faces thereof, said second element including low pressure inlet means to allow the introduction of low pressure fluid into said cells, high pressure outlet means to allow the extraction of high pressure fluid from said cells, said high pressure outlet means and said low pressure inlet means being circumferentially spaced from each other and both positioned adjacent one face of said first element, with one of said clearance spaces therebetween, low pressure outlet means to allow the extraction of low pressure fluid from said cells and high pressure inlet means to allow the introduction of high pressure fluid into said cells, said low pressure outlet means and said high pressure inlet means being circumferentially spaced from each other and both positionedadjacent said other face of said first element, with another of said clearance spaces therebetween, said low pressure inlet and outlet means together defining a low pressure scavenging zone and said high pressure inlet and outlet means together defining a high pressure scavenging zone, in which latter zone the scavenging of said cells is incomplete, the pressure exchanger further comprising a source of sealing fluid at a pressure higher than that in one of said clearance spaces and passage means interconnecting said source to said one clearance space.

8. A pressure exchanger as claimed in claim 7 in which said source is provided by one of said cells,

9. A pressure exchanger as claimed in claim 7 in which said source is provided by one of said inlet and outlet means.

10. A pressure exchanger comprising in combination a first and a second element mounted co-axially for relative rotation, a plurality of clearance spaces between said elements and means for effecting said relative rotation, said first element defining a ring of open-ended cells extending therethrough between two opposed faces thereof, said second element including low pressure inlet means to allow the introduction of low pressure fluid into said cells, high pressure outlet means to allow the extraction of high pressure fluid from said cells, said high pressure outlet means and said low pressure inlet means being circumferentially spaced from each other and both positioned adjacent one face of said first element, with another of said clearance spaces therebetween, low pressure outlet means to allow the extraction of low pressure fluid from said cells and high pressure inlet means to allow the introduction of high pressure fluid into said cells, said low pressure outlet means and said high pressure inlet means being circumferentially spaced from each other and both positioned adjacent said other face of said first element, said low pressure inlet and said outlet means together defining a low pressure scavenging zone and said high pressure inlet and outlet means together defining a high pressure scavenging zone, in which latter zone the scavenging of said cells is incomplete, the pressure exchanger further comprising, a plurality of sources of sealing fluid, and a plurality of passage means each interconnecting one of said sources to one of said clearance spaces, the pressure of the sealing fluid in each of said sources being higher than that in the clearance space to which it is connected.

11. A pressure exchanger as claimed in claim 10 in which each of said sources is provided by one of said cells, inlet means and outlet means.

12. A pressure exchanger comprising a rotor, a ring of axially extending open-ended cells for the compression and expansion of gas mounted peripherally on said rotor, stationary end plates spaced apart from the cell ends, and clearance spaces between said end plates and said rotor permitting rotation of the rotor, ducting in said end plates for leading gas to and from said cells, annular flanges extending from said end plates and embracing in a telescopic manner said rotor, annular clearance spaces between said flanges and said rotor and means for rotating the rotor, said ducting including in one of said end plates a high pressure introduction passage for high pressure gas and a low pressure extraction passage for low pressure gas, said passages being spaced apart circumferentially of the rotor, and in the other end plate a low pressure introduction passage for low pressure gas and a high pressure extraction passage for high pressure gas, said latter passages being spaced apart circumferentially of the rotor, said high pressure introduction and extraction passages together forming a high pressure scavenging zone in which the scavenging of cells is incomplete and said low pressure introduction and extraction passages together forming a low pressure scavenging zone in which the scavenging of cells is substantially complete, the pressure exchanger further comprising sealing gas conduits connecting said high pressure extraction passage to said annular clearance spaces and said end clearance spaces.

13. The combination of a pressure exchanger and an internal combustion engine to be supercharged by said pressure exchanger, in which combination said internal combustion engine includes an induction manifold and an exhaust manifold and said pressure exchanger comprises a first element and a second element mounted coaxially for relative rotation and means for effecting said relative rotation, said first element defining a ring of open-ended cells extending therethrough between two opposed faces thereof, said second element including low pressure inlet means to allow the introduction of low pressure fluid into said cells, high pressure outlet means to allow the extraction of high pressure fluid from said cells, said high pressure outlet means and said low pressure inlet means being circumferentially spaced from each other and both positioned adjacent one face of said first element, low pressure outlet means to allow the extraction of low pressure fluid from said cells and high pressure inlet means to allow the introduction of high pressure fluid into said cells, said low pressure outlet means and said high pressure inlet means being circumferentially spaced from each other and both positioned adjacent said other face of said first element, said low pressure inlet and outlet means together defining a low pressure scavenging zone and said high pressure inlet and outlet means together defining a high pressure scavenging zone, in which latter zone the scavenging of said cells is incomplete, the combination also including first duct means connecting said high pressure outlet means to said induction manifold and second duct means connecting said high pressure inlet means to said exhaust manifold, said low pressure inlet and outlet means being open to atmosphere.

References Cited in the file of this patent UNITED STATES PATENTS 2,081,149 Meininghans May 25, 1937 2,675,173 Jendrassik Apr. 13, 1954 FOREIGN PATENTS 2,818 Great Britain 1906 

